US Federal Reserve chief Janet Yellen told the Senate Banking Committee that policymakers thought severe weather across much of the country was to blame for a disappointing run of economic data over the past two months, including on jobs, industrial output and consumption.

However, she said they would be keeping a close eye on the economy to see if the weak figures continue, which could lead to a slower pace of cuts to the stimulus programme.

Investors are also keeping an eye on the crisis in Ukraine, a major energy consumer where ousted pro-Moscow president Viktor Yanukovych emerged defiant on Thursday after five days in hiding.

Singapore's United Overseas Bank said in a market commentary that investors were fretting over weaker US data and the ongoing uncertainties in Ukraine.